Such a method is used for example in a thermal transfer printer whose print head has printing elements arranged next to one another in a row. Between the print head and a graphics carrier to be printed upon is arranged a heat sensitive color tape which upon pointwise heating by a heating element above a printing temperature transfers a color point to the graphics carrier. A relative movement is created between the print head and the graphics carrier perpendicularly to the line of the printing elements. In predetermined time intervals designated heating elements are then energized with current and a printing event is effected. The graphics carrier is thereby printed in a raster way with characters or a pattern.
In a method known from DE 38 33 746 A1 the heating element is preheated if no printing event is effected. Current impulses are delivered to the heating element whose energy content heats the heating element to a temperature below the printing temperature. The amplitude and duration of the impulses can be controlled in dependence on the prevailing surrounding temperature and the constructional formation of the printing head. It is thereby achieved that the preheating temperature is uniformly distributed over the entire printing head area.
In this known method the energy delivered to each heating element for preheating is adjusted independently of whether the involved heating element often or seldom effects printing events. Since a high printing frequency at the printing element establishes a higher temperature than does a low printing frequency the average preheating temperature distributed over the entire printing head must lie distinctly below the printing temperature, so that even at high printing demands of the heating elements trouble-free printing will be achieved. This has the result that to effect a printing event the current impulse delivered to the heating element must have a high energy content in order that the heating element is heated to its printing temperature. The creation of such current impulse is technically expensive since the current impulse generator necessary therefor must have a high peak load capability.
In addition, in the case of a large temperature difference between the preheating temperature and the printing temperature the times required for the heating process and for cooling are also long. These times influence in great measure the printing speed achievable with the printing method. Since in the known method a sufficiently high temperature difference is necessary between the preheating temperature distributed uniformly over the entire print head area and the printing temperature to create the desired printing quality, the achievable printing speed is limited to a low value.